Activation and differentiation of cognate T cells by a dextran-based antigen-presenting system for cancer immunotherapy.

Immunotherapeutic modulation of antigen-specific T-cell responses instead of the whole repertoire helps avoid immune-related adverse events. We have developed an artificial antigen-presenting system (aAPS) where multiple copies of a multimeric peptide-MHC class I complex presenting a murine class I MHC restricted ovalbumin-derived peptide (signal 1), along with a costimulatory ligand (signal 2) are chemically conjugated to a dextran backbone. Cognate naive CD8+ T cells, when treated with this aAPS underwent significant expansion and showed an activated phenotype. Furthermore, elevated expression of effector cytokines led to the differentiation of these cells to cytotoxic T lymphocytes which resulted in target cell lysis, indicative of the functional efficacy of the aAPS. CD8+ T cells with decreased proliferative potential due to repeated antigenic stimulation could also be re-expanded by the developed aAPS. Thus, the developed aAPS warrants further engineering for future application as a rapidly customizable personalized immunotherapeutic agent, incorporating patient-specific MHC-restricted tumor antigens and different costimulatory signals to modulate both naive and antigen-experienced but exhausted tumor-specific T cells in cancer.

Fluorescently labelled thioacetazone for detecting the interaction with Mycobacterium dehydratases HadAB and HadBC.

Thioacetazone (TAC) used to be a highly affordable, bacteriostatic anti-TB drug but its use has now been restricted, owing to severe side-effects and the frequent appearance of the TAC resistant M. tuberculosis strains. In order to develop new TAC analogues with fewer side-effects, its target enzymes need to be firmly established. It is now hypothesized that TAC, after being activated by a monooxygenase EthA, binds to the dehydratase complex HadAB that finally leads to a covalent modification of HadA, the main partner involved in dehydration. Another dehydratase enzyme, namely HadC in the HadBC complex, is also thought to be a possible target for TAC, for which definitive evidence is lacking. Herein, using a recently exploited azido naphthalimide template attached to thioacetazone and adopting a photo-affinity based labelling technique, coupled with electrophoresis and in-gel visualization, we have successfully demonstrated the involvement of these enzymes including HadBC along with a possible participation of an alternate mycobacterial monooxygenase MymA. In silico studies also revealed strong interactions between the TAC-probe and the concerned enzymes.

Electron deficient borane-mediated hydride abstraction in amines: stoichiometric and catalytic processes.

The manipulation of amino C-H bonds has garnered significant interest from the synthetic community due to its inherently high atom, step and redox economy. This Tutorial Review summarises the ability of boranes to mediate hydride abstraction from α-amino and γ-amino conjugated C-H bonds. Borane-mediated hydride abstraction results in the generation of reactive iminium hydridoborate salts that participate in a variety of stoichiometric and catalytic processes. The reactions that have utilised this unusual reactivity include those that manipulate amino scaffolds (including dehydrogenation, racemisation, isomerisation, α- and ß-functionalisation, and C-N bond cleavage) and those that use amine-based reagents (transfer hydrogenation, and alkylation).

How To Achieve High Regioselectivity in Barrier-less Nucleophilic Addition to p-Benzynes Generated via Bergman Cyclization of Unsymmetrical Cyclic Azaenediyne?

Inducing high regioselectivity in nucleophilic addition to p-benzynes, first reported by Perrin and O'Connor et al. ( J. Am. Chem. Soc. 2007 , 129 , 4795 - 4799 ) has been a challenge as the reaction involves a very fast barrier-less addition of nucleophile. On the other hand, achieving a high degree of regioselectivity is important as that will make the reaction synthetically useful. Recently, a study has been reported from our group ( J. Org. Chem. 2018 , 83 , 7730 - 7740 ), whereby it was shown that nucleophilic addition to p-benzynes derived from unsymmetrical N-substituted cyclic enediynes proceeds with low extent of selectivity by incorporation of groups with divergent electronic characters. Herein, we report that excellent regioselectivity (>99%) can be achieved keeping an ortho alkoxy group in unsymmetrical 1,2-dialkynylbenzene in the form of a cyclic enediyne in quantitative yields. High regioselectivity (∼84%) is also shown by pyridine based enediynes where the pyridine nitrogen is in a 1,3-relationship with the impending radical center, expanding the synthetic scope of this nucleophilic addition. The regioselectivity can be explained in terms of computed electrostatic potentials which are substantially different around two radical centers arising due to the "ortho effect" (conformational alignment of lone pair of the ortho alkoxy oxygen or the nitrogen in pyridine systems).

Experiment and Computational Study on the Regioselectivity of Nucleophilic Addition to Unsymmetrical p-Benzynes Derived from Bergman Cyclization of Enediynes.

The regioselectivity in addition of nucleophiles to the p-benzyne intermediates derived from unsymmetrical aza-substituted enediynes via Bergman cyclization was studied. Computational studies [using UB3LYP/6-31G(d,p) level of theory] suggest that the p-benzyne intermediate retains its similar electrophilic character at the two radical centers even under unsymmetrical electronic perturbation, thus supporting the predicted model of nucleophilic addition to p-benzyne proposed by Perrin and co-workers (Perrin et al. J. Am. Chem. Soc. 2007, 129, 4795-4799) and later by Alabugin and co-workers (Peterson et al. Eur. J. Org. Chem. 2013, 2013, 2505-2527). However, observed experimental results suggest that there was small but definite regioselectivity (∼5-25%), the extent varying with the electronic nature of the substituents. Differential solvated halide ion concentrations around the vicinity of two radical centers arising due to surrounding surface electrostatic potential (computationally calculated) may be one of the possible factors for such selectivity in some of the examined p-benzynes. However, other complicated dynamical issues like the trajectory of the attacking nucleophile to the radical center which can be influenced by electronic and/or steric perturbation of starting enediyne conformation cannot be ruled out. The overall yield of the anionic addition was in the range of 80-99%.

Applications of [4+2] Anionic Annulation and Carbonyl-Ene Reaction in the Synthesis of Anthraquinones, Tetrahydroanthraquinones, and Pyranonaphthoquinones.

Hexa-2,5-dienoates, susceptible to isomerization by acids and bases, are suitable for the [4+2] anionic annulation to give 3-(2-alkenyl)naphthoates in regiospecific manner. When combined with intramolecular carbonyl-ene reaction (ICE), the accessibility of the naphthoates culminates in a new synthesis of anthraquinones and diastereoselective synthesis of tetrahydroanthraquinones. This strategy has also resulted in a 3-step synthesis of dehydroherbarin from a 3-methallylnaphthoate.

Thiophene-fused γ-lactams inhibit the SARS-CoV-2 main protease via reversible covalent acylation.

Enzyme inhibitors working by O-acylation of nucleophilic serine residues are of immense medicinal importance, as exemplified by the ß-lactam antibiotics. By contrast, inhibition of nucleophilic cysteine enzymes by S-acylation has not been widely exploited for medicinal applications. The SARS-CoV-2 main protease (Mpro) is a nucleophilic cysteine protease and a validated therapeutic target for COVID-19 treatment using small-molecule inhibitors. The clinically used Mpro inhibitors nirmatrelvir and simnotrelvir work via reversible covalent reaction of their electrophilic nitrile with the Mpro nucleophilic cysteine (Cys145). We report combined structure activity relationship and mass spectrometric studies revealing that appropriately functionalized γ-lactams can potently inhibit Mpro by reversible covalent reaction with Cys145 of Mpro. The results suggest that γ-lactams have potential as electrophilic warheads for development of covalently reacting small-molecule inhibitors of Mpro and, by implication, other nucleophilic cysteine enzymes.

B(C6F5)3-Catalyzed Direct C3 Alkylation of Indoles and Oxindoles.

The direct C3 alkylation of indoles and oxindoles is a challenging transformation, and only a few direct methods exist. Utilizing the underexplored ability of triaryl boranes to mediate the heterolytic cleavage of α-nitrogen C-H bonds in amines, we have developed a catalytic approach for the direct C3 alkylation of a wide range of indoles and oxindoles using amine-based alkylating agents. We also employed this borane-catalyzed strategy in an alkylation-ring opening cascade.